1. Field of the Invention
The present invention relates to a thin-film transistor device.
More particularly, the invention relates to a thin-film transistor device that has an insulating interlevel wiring dielectric layer formed simultaneously with a gate insulating layer.
2. Background Art
Thin-film transistors which employ thin amorphous semiconductor films as active layers are increasingly used as switching devices or as circuits for driving image sensors because they are easy to fabricate. Also, devices with a large area can be easily manufactured.
In forming an array of thin-film transistors which comprises a plurality of thin-film transistors arranged on a single substrate, it is often required to provide a multi-level wiring section by such means as matrix wiring. A multi-level wiring section is commonly produced by the following method. A gate array of thin-film transistors and a first wiring layer are formed. Then, thin-film transistors are formed by successively depositing a gate insulating layer, an active layer, a source electrode and a drain electrode. Thereafter, an insulating interlevel dielectric layer and a second wiring layer are successively deposited.
The interlevel insulating dielectric layer in the multi-level wiring section is conventionally formed of an organic film made of a polymer such as polyimide The polyimide film can be deposited with a highly flat surface so that, unlike an inorganic film made of silicon oxide or other inorganic materials, it will not increase the unevenness already introduced by the thickness of the first level pattern. This flatness serves to ensure the integrity of the second level pattern which would otherwise be interrupted at step edges of the first level pattern to thereby impair the reliability of the device.
The polyimide film, however, has the disadvantage of being highly susceptible to pin hole formation and a dual structure must be employed in order to prevent unwanted shorts between the first and second level patterns. But the provision of a double-layered polyimide film increases the complexity of the device fabrication process.